Ken, if I'm correct the output from the l.o. mixer , port 26, should be pretty
much the same on all bands? I do have a good scope but do not have a good
signal generator. I used to have all that quality equipment on the job, but I
have been retired from the business for 13 yrs. The l.o. mixer board is nested
below a cover which has another board mounted on the top, making it almost
impossible, with out a wiring harness, to make live checks. I have made ohm
meter check of of the switching coming into the board and all looks okay. I've
checked the diodes at the output of of u2 feeding the bandpass filters and they
are all okay. I've not checked the solder joints. I do wonder about u2
(udn2985, 8 ch. source driver) though it is rare to have that type of failure
with a I.C. if it has not taken some kind of abuse.
Thanks for the input and I will take the board out and check the solder joints
with a magnify glass.
Wayne
________________________________
From: Ken Brown <ken.d.brown@hawaiiantel.net>
To: geraldj@weather.net; Discussion of Ten-Tec Equipment <tentec@contesting.com>
Sent: Sat, November 27, 2010 3:20:06 PM
Subject: Re: [TenTec] Omni 6+ - no output on 12M/10M and omni 6+/ power issue
> Low or no output on a band or bands can be dirty switch contacts. 10,
> 12, and 15 haven't had much use in the past few year. It might be a
> quarter drop of deoxit on each contact with some vigorous switch
> operation might clean them up, or the problem could be a poor solder
> joint that went open or nearly open.
>
The Omni VI uses diode switching for all of that. I don't think there is
a single mechanical switch contact (besides the band select push button)
involved with the band selection. If it indicates that it has switched
to the band you want, then that pushbutton is working fine. The parallel
band select lines that go to various boards may need cleaning and the
bad solder joint is a possibility.
>
> Its not possible to be more specific because there can be so many ways
> to loose a band or bands (and the crystal is not above suspicion nor the
> crystal socket when crystals are used to heterodyne the VFO) unless one
> has repaired many Omni VI with the same problem. I doubt there's any RF
> difference between VI and VI+.
>
Omni VI does not use crystal sockets. A bad crystal, or misaligned
inductor in the crystal oscillator circuit could be the cause. Don't
mess with those inductors unless you have the right equipment to get
yourself out of the trouble you may cause. The locations of the coils
used for each band is not immediately obvious, and there is a good
chance you'll end up adjusting one that did not need adjusting. Make
sure you use the perfectly shaped soft plastic twiddle stick for the
inductor slug or you will likely break the slug. You will need an
oscilloscope with a high impedance probe (like a 10 X probe that only
loads the circuit with 10 Meg ohms + small capacitance) to monitor the
PLL loop in order to properly set those slugs. And when you have that
equipment, the description of the waveform you are looking for is more
than I'm prepared to put in this message.
DE N6KB
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